Fuel cells are an emerging technology that can significantly improve energy efficiency and energy security. Fuel cell technology can provide environmentally friendly electrical energy, producing far fewer harmful pollutants and lower levels of noise than conventional power generation systems. Although various types of fuel cells have been installed for commercial use, high manufacturing costs have largely prohibited them from being accepted for a wide variety of applications.
In addition to high manufacturing cost, the fuel cell industry is faced with several critical challenges that must be resolved before fuel cell systems can be fully commercialized for wide spread power generation applications. These challenges include, for example, a need to identify anode, electrolyte and cathode materials that provide lower electrochemical losses, a need for durable fuel cell interconnects, improved sealing concepts, compatible metallic interconnects, advanced stack cooling, low-cost fabrication processes, understanding soot and carbon deposit mechanisms, efficient fuel processor and regenerative desulfurization systems.
Among various types of fuel cells, the solid oxide fuel cell (SOFC) appears to exhibit many advantages over other fuel cell systems for power generation. For example, SOFCs have the highest energy efficiency of known fuel cells due to their high temperature operation. SOFCs can also tolerate low-cost catalytic materials. Existing studies indicate that SOFCs are probably one of the most reliable power generation technologies. SOFCs are well suited for integration with conventional gas turbine engines for improvements in fuel consumption and emission pollution. In addition, SOFCs can be supplied with hydrogen gas via hydrocarbon injector/reformer systems that convert hydrocarbon fuels into hydrogen gas and carbon monoxide, known as syngas, allowing full utilization of the existing refueling infrastructure. Because of these significant advantages, the fuel cell industry has been working diligently to develop compact, efficient fuel processors that can effectively convert the liquid hydrocarbon fuels into hydrogen-rich gas for utilization in SOFCs as well as other fuel cell systems.
Fuel processors are a very important component of SOFC systems, enabling them to compete with the conventional auxiliary power units (APU) in remote stationary and mobile power generation markets. Current state-of-the-art fuel processors are limited to using gaseous fuels, such as natural gas, hydrogen and liquefied petroleum gas (LPG). In the near term, however, liquid hydrocarbon fuels are the preferred choice for SOFC power systems because of their availability, high energy density, and existing distribution networks.
Currently, liquid fuel processing technology is not yet viable for commercial applications in SOFC systems. One technical barrier for liquid fuel processing is reactor durability. The performance of the reforming catalysts quickly deteriorates as a result of carbon deposition, sulfur poisoning and loss of precious metals due to sintering or evaporation at high temperatures. To mitigate these problems, numerous studies are being conducted to optimize catalyst materials and reactor design and operation.
One engineering approach that could alleviate problems associated with liquid fuel processing is improvement of feed stream preparation. Poor feed stream preparation such as inadequate atomization, wall impingement, and non-uniform mixing can easily lead to local conditions that favor carbon deposition and formation of hot spots in the reactor. Because liquid fuels are difficult to reform, a proper selection of injection and mixing systems for feed stream preparation plays an essential role in the development of reliable and durable liquid fuel processors.
In a typical fuel processor, liquid fuel is injected into preheated gas (e.g., steam and/or air) streams near the top of a mixing chamber. The liquid fuel must evaporate and be thoroughly mixed with the surrounding gas within a short distance prior to entering the catalytic reactor. During operation, the injection and mixing system must be able to accommodate varying power demands in a relatively short response time. In most mobile APU applications, there are very limited supply pressures available for liquid atomization and feed stream mixing, making it especially challenging for the design and development of fuel injection and mixing systems.
It is desirable to provide an injection and mixing system that can be easily integrated into various types of fuel processors. The fuel injection and mixing system must demonstrate better mixing capability and be more compact in size with fewer components and lower manufacturing cost than existing systems. It is also desirable to provide an injection and mixing system that requires very low supply pressures and energy power consumption. Finally, it would be desirable to provide an injection and mixing system that can demonstrate extended service life without the problem of carbon or coke deposition.
As will be shown herein, the present invention provides a solution for the problems and needs identified above.